A first group invention of the present invention relates to an NiCuZn-based ferrite material having an initial permeability xcexci of not lower than 200, particularly to a ferrite material having good temperature dependence of initial permeability, a high quality coefficient Q and high strength. The ferrite material of the present invention can be suitably used in, for example, a resin-mold-type ferrite component.
Further, a second group invention of the present invention relates to an NiCuZn-based ferrite material having an initial permeability xcexci of not higher than 100, particularly to a ferrite material having good temperature dependence of initial permeability, a high quality coefficient Q and high strength. The ferrite material of the present invention can be suitably used in, for example, a resin-mold-type ferrite component.
Still further, a third group invention of the present invention relates to an NiCuZn-based ferrite material as described above, particularly to a ferrite material used in a resin-mold-type ferrite component.
(1) In recent years, demands for components such as resin-mold-type chip inductor and stationary coil are rapidly growing in the fields of a television, a video recorder, a mobile communication device and the like. The products in such fields are demanded to have such characteristics as a small size, light weight and high accuracy, and along with the demand, demands for a decrease in tolerance and an increase in reliability to the above components are growing.
Meanwhile, a ferrite is commonly used in the core material of these components. In the case of a resin-mold-type inductor component, a compressive stress is produced in the core by resin molding, and the inductance value of the ferrite changes according to this compressive stress. Therefore, it is difficult to obtain a high-quality resin-mold-type inductor component having small inductance tolerance.
Under the circumstances, a ferrite which undergoes a small change in inductance when an external force is applied, that is, a ferrite having good stress resistance is desired. Further, to increase the reliability of a device using an inductance component, it is important to increase the reliability of the inductance component itself, specifically, to decrease the temperature dependence of initial permeability of the ferrite used in the inductance component.
In response to such a demand, a variety of improvement techniques in this field have heretofore been made. That is, in Japanese Patent Application Laid-Open No. 326243-1993, an NiCuZn-based ferrite containing 0.05 to 0.60 wt % of Co3O4, 0.5 to 2 wt % of Bi2O3 and 0.10 to 2.00 wt % of a combination of SiO2 and SnO2 is proposed. However, since the NiCuZn-based ferrite contains a small amount of ZnO, a high initial permeability of not lower than 200 cannot be obtained.
Further, in Japanese Patent No. 267916, an NiCuZn-based ferrite containing 0.05 to 0.60 wt % of Co3O4, 3 to 5 wt % of Bi2O3 and 0.10 to 2.00 wt % of SiO2 is proposed. However, since the NiCuZn-based ferrite contains a small amount of ZnO, a high initial permeability of not lower than 200 cannot be obtained.
Further, in Japanese Patent Application Laid-Open No. 103953-1989, an NiZn based ferrite containing 0.05 to 2 wt % of Bi2O3, 0 to 1 wt % of SiO2 and MgO or an oxide of Mn is proposed. Although the NiZn based ferrite has improved heat shock resistance, its temperature dependence of initial permeability cannot be said to be satisfactory.
Further, in Japanese Patent Application Laid-Open No. 228108-1989, an NiCuZn-based ferrite containing SiO2 in an amount of 0.03 wt % or less, MnO in an amount of 0.1 wt % or less, Bi2O3 in an amount of 0.1 wt % or less and MgO in an amount of 0.1 wt % or less to form a structure for alleviating the stress is proposed. However, since the NiCuZn-based ferrite contains a small amount of Bi2O3, its stress resistance cannot be said to be satisfactory.
Further, in Japanese Patent Application Laid-Open No. 325056-1996, an NiZn based ferrite material containing CoO, Bi2O3 and SiO2 to make a change in inductance under a load extremely small and increase a Q value at high frequency is disclosed.
However, as seen in the example disclosed in the gazette, the main composition of the example is out of the range of the main composition of the present invention and does not include MgO of the present invention. Therefore, the value of a quality coefficient Q is liable to be low.
In addition, in the case of a conventional NiCuZn ferrite containing Bi2O3 and having high initial permeability, since its grain size diameter is large, a temperature coefficient is low and the Q is high, so that a ferrite component having high strength cannot be obtained.
(2) As described above, in recent years, demands for components such as resin-mold-type chip inductor and stationary coil are rapidly growing in the fields of a television, a video recorder, a mobile communication device and the like. The products in such fields are demanded to have such characteristics as a small size, light weight and high accuracy, and along with the demand, demands for a decrease in tolerance and an increase in reliability to the above components are growing.
Meanwhile, a ferrite is commonly used in the core material of these components. In the case of a resin-mold-type inductor component, a compressive stress is produced in the core by resin molding, and the inductance value of the ferrite changes according to this compressive stress. Therefore, it is difficult to obtain a high-quality resin-mold-type inductor component having small inductance tolerance.
Under the circumstances, a ferrite which undergoes a small change in inductance when an external force is applied, that is, a ferrite having good stress resistance is desired. Further, to increase the reliability of a device using an inductance component, it is important to increase the reliability of the inductance component itself, specifically, to decrease the temperature dependence of initial permeability of the ferrite used in the inductance component.
In response to such a demand, a variety of improvement techniques in this field have heretofore been made. That is, in Japanese Patent Application Laid-Open No. 326243-1993, an NiCuZn-based ferrite containing 0.05 to 0.60 wt % of Co3O4, 0.5 to 2 wt % of Bi2O3 and 0.10 to 2.00 wt % of a combination of SiO2 and SnO2 is proposed. However, although the NiCuZn-based ferrite has improved stress resistance, Q is low and its temperature dependence of initial permeability is not satisfactory, either.
Further, in Japanese Patent No. 267916, an NiCuZn-based ferrite containing 0.05 to 0.60 wt % of Co3O4, 3 to 5 wt % of Bi2O3 and 0.10 to 2.00 wt % of SiO2 is proposed. However, as in the case of the above ferrite, its temperature dependence of initial permeability cannot be said to be satisfactory and its quality coefficient Q is also low.
Further, in Japanese Patent Application Laid-Open No. 103953-1989, an NiZn based ferrite containing 0.05 to 2 wt % of Bi2O3, 0 to 1 wt % of SiO2 and MgO or an oxide of Mn is proposed. Although the NiZn based ferrite has improved heat shock resistance, its temperature dependence of initial permeability cannot be said to be satisfactory and its quality coefficient Q is also low.
Further, in Japanese Patent Application Laid-Open No. 228108-1989, an NiCuZn based ferrite containing SiO2 in an amount of 0.03 wt % or less, MnO in an amount of 0.1 wt % or less, Bi2O3 in an amount of 0.1 wt % or less and MgO in an amount of 0.1 wt % or less to form a structure for alleviating the stress is proposed. However, since the NiCuZn-based ferrite contains a small amount of Bi2O3, neither sufficient strength nor sufficient temperature dependence of initial permeability is obtained.
Further, in Japanese Patent Application Laid-Open No. 325056-1996, an NiZn based ferrite material containing CoO, Bi2O3 and SiO2 to make a change in inductance under a load extremely small and increase the Q value at high frequency is disclosed.
However, as seen in the example disclosed in the gazette, the main composition of the example is out of the range of the main composition of the present invention and does not include MgO of the present invention. Therefore, the value of the quality coefficient Q is liable to be low.
(3) A nickel-based ferrite material (such as an NiCuZn-based ferrite, NiCu-based ferrite or Ni-based ferrite) is widely used as an inductor element. Meanwhile, along with rapid developments in the fields of information and telecommunication and high frequency in recent years, demand for an improvement in the performance of a resin-mold-type inductor element or the like.
When the resin-mold-type inductor element is prepared, a ferrite material is molded into a resin, and a compressive stress is exerted on the ferrite material when the resin is cured. Since the inductance value of the ferrite material changes according to the degree of the compressive stress, a ferrite material which exhibits a small inductance change caused by the compressive stress and has excellent stress resistance is desired for the resin-mold-type inductor element. As for the improvements in the performance of the inductor element, a gentle change in permeability along with a change in temperature and a large Q value which is a quality coefficient in a frequency band used are desired.
To respond to such desires, an NiCuZn-based ferrite material containing cobalt oxide, bismuth oxide and silicon oxide is disclosed in Japanese Patent No. 2679716, Japanese Patent Application Laid-Open No. 326243-1993 and the like. Further, an NiZn-based ferrite material containing bismuth oxide and silicon oxide to have heat shock resistance improved is disclosed in Japanese Patent Application Laid-Open No. 103953-1989, and an NiCuZn-based ferrite material containing silicon oxide, manganese oxide, bismuth oxide and magnesium oxide to have a stress-alleviating structure is disclosed in Japanese Patent Application Laid-Open No. 228108-1989. Further, a heat-shock-resistant ferrite material having an average grain size diameter of crystal structure of 20 to 60 xcexcm is disclosed in Japanese Patent Application Laid-Open No. 323806-1992, and an NiCuZn-based ferrite material containing 2.1 to 10.0 wt % of silicon oxide is disclosed in Japanese Patent Application Laid-Open No. 325056-1996.
However, the above NiCuZn-based ferrite material disclosed in Japanese Patent No. 2679716 and Japanese Patent Application Laid-Open No. 326243-1993 contains zinc oxide in a small amount of 2 to 30 mol %, so that high initial permeability xcexci cannot be obtained. Further, the NiZn based ferrite material disclosed in Japanese Patent Application Laid-Open No. 103953-1989 contains a small amount of cobalt oxide, so that a change in permeability along with a change in temperature is large, and the NiCuZn-based ferrite material disclosed in Japanese Patent Application Laid-Open No. 228108-1989 contains bismuth oxide in an amount of 0.1 wt % or less, so that its stress resistance is not satisfactory. Further, the heat-shock-resistant ferrite material disclosed in Japanese Patent Application Laid-Open No. 323806-1992 has a large average grain size diameter of crystal structure of 20 to 60 xcexcm, so that a change in permeability along with a change in temperature is large, and the NiCuZn-based ferrite material disclosed in Japanese Patent Application Laid-Open No. 325056-1996 contains a large amount of silicon oxide, so that a change in permeability along with a change in temperature is large.
Therefore, a ferrite material having high initial permeability, excellent stress resistance and a low absolute value of temperature coefficient is desired.
The present invention has been invented to solve the above problems of the prior art.
That is, the first group invention of the present invention has been invented for solving the problem in the above (1) of the prior art. An object thereof is to solve the problem of the above (1) and provide an NiCuZn-based ferrite material having a high initial permeability of not lower than 200, good temperature dependence of initial permeability, a high quality coefficient Q and high strength.
To achieve such an object, the present invention is an NiCuZn-based ferrite material containing, as main components, an iron oxide in an amount of 47.0 to 50.0 mol % in terms of Fe2O3, a manganese oxide in an amount of 0.3 to 1.5 mol % in terms of Mn2O3, a copper oxide in an amount of 2.0 to 8.0 mol % in terms of CuO, zinc oxide in an amount of 30.1 to 33.0 mol % in terms of ZnO and a nickel oxide (NiO) in mol % as the balance, wherein 0.5 to 6.0 wt % of bismuth oxide in terms of Bi2O3, 0.1 to 2.0 wt % of silicon oxide in terms of SiO2 and 0.05 to 1.0 wt % of magnesium oxide in terms of MgO are further contained in addition to the main components.
Further, the present invention is an NiCuZn-based ferrite material containing, as main components, an iron oxide in an amount of 47.0 to 50.0 mol % in terms of Fe2O3, a manganese oxide in an amount of 0.3 to 1.5 mol % in terms of Mn2O3, a copper oxide in an amount of 2.0 to 8.0 mol % in terms of CuO, zinc oxide in an amount of 30.1 to 33.0 mol % in terms of ZnO and a nickel oxide (NiO) in mol % as the balance, wherein 0.5 to 6.0 wt % of bismuth oxide in terms of Bi2O3 and 0.15 to 3.2 wt % of talc are further contained in addition to the main components.
Further, the present invention has an initial permeability xcexci at a frequency of 100 kHz of not lower than 200.
The second group invention of the present invention has been invented for solving the problem in the above (2) of the prior art. An object thereof is to solve the problem of the above (2) and provide an NiCuZn-based ferrite material which undergoes an extremely small change in inductance when an external force is applied and which has excellent stress resistance, good temperature dependence of initial permeability and a high quality coefficient Q.
To achieve such an object, the present invention is an NiCuZn-based ferrite material containing, as main components, an iron oxide in an amount of 47.0 to 50.0 mol % in terms of Fe2O3, a manganese oxide in an amount of 0.01 to 3.0 mol % in terms of Mn2O3, a copper oxide in an amount of 0.5 to 4.9 mol % in terms of CuO, zinc oxide in an amount of 1.0 to 23.0 mol % in terms of ZnO and a nickel oxide in mol % in terms of NiO as the balance, wherein 0.02 to 1.0 wt % of cobalt oxide in terms of CoO, 0.5 to 10.0 wt % of bismuth oxide in terms of Bi2O3, 0.1 to 2.0 wt % of silicon oxide in terms of SiO2 and 0.05 to 1.0 wt % of magnesium oxide in terms of MgO are further contained in addition to the main components.
Further, the present invention is an NiCuZn-based ferrite material containing, as main components, an iron oxide in an amount of 47.0 to 50.0 mol % in terms of Fe2O3, a manganese oxide in an amount of 0.01 to 3.0 mol % in terms of Mn2O3, a copper oxide in an amount of 0.5 to 4.9 mol % in terms of CuO, zinc oxide in an amount of 1.0 to 23.0 mol % in terms of ZnO and a nickel oxide in mol % in terms of NiO as the balance, wherein 0.02 to 1.0 wt % of cobalt oxide in terms of CoO, 0.5 to 10.0 wt % of bismuth oxide in terms of Bi2O3 and 0.15 to 3.2 wt % of talc are further contained in addition to the main components.
Further, the present invention has an initial permeability xcexci at a frequency of 100 kHz of not higher than 100.
The third group invention of the present invention has been invented for solving the problem in the above (3) of the prior art. An object thereof is to provide an inexpensive ferrite material which has high initial permeability and excellent stress resistance and which exhibits a small inductance change caused by a compressive stress and a gentle change in permeability along with a change in temperature.
To achieve such an object, the ferrite material of present invention is a ferrite material containing an iron oxide, a copper oxide, zinc oxide and a nickel oxide as main components, wherein the iron oxide is contained in an amount of 46.0 to 49.0 mol % in terms of Fe2O3, the copper oxide is contained in an amount of 4.0 to 11.0 mol % in terms of CuO, the zinc oxide is contained in an amount of 30.1 to 33.0 mol % in terms of ZnO and the nickel oxide is contained as the balance, and in addition to these main components, 0.005 to 0.03 wt % of cobalt oxide in terms of CoO, 0.1 to 0.5 wt % of bismuth oxide in terms of Bi2O3, 0.1 to 0.6 wt % of silicon oxide in terms of SiO2 and 0.05 to 1.0 wt % of magnesium oxide in terms of MgO are further contained as additional components.
Further, the ferrite material of the present invention is a ferrite material containing an iron oxide, a copper oxide, zinc oxide and a nickel oxide as main components, wherein the iron oxide is contained in an amount of 46.0 to 49.0 mol % in terms of Fe2O3, the copper oxide is contained in an amount of 4.0 to 11.0 mol % in terms of CuO, the zinc oxide is contained in an amount of 30.1 to 33.0 mol % in terms of ZnO and the nickel oxide is contained as the balance, and in addition to these main components, 0.005 to 0.03 wt % of cobalt oxide in terms of CoO, 0.1 to 0.5 wt % of bismuth oxide in terms of Bi2O3 and 0.1 to 2.0 wt % of talc are further contained as additional components.
Further, the above ferrite material has an initial permeability at a frequency of 100 kHz of not lower than 200.
Further, the above ferrite material has a relative coefficient of temperature dependence of initial permeability in a range of xc2x15 (ppm/xc2x0 C.).
In addition, the above ferrite material has a rate of change in inductance under a pressure of 98 MPa in a range of xc2x15%.
A detailed description will be given to the embodiments of the present invention hereinafter.
(1) Description of the Invention of the First Invention Group
A detailed description will be given to the ferrite material of the present invention hereinafter. The ferrite material of the present invention contains, as its substantial main components, an iron oxide in an amount of 47.0 to 50.0 mol % (particularly preferably 47.5 to 49.5 mol %) in terms of Fe2O3, a manganese oxide in an amount of 0.3 to 1.5 mol % (particularly preferably 0.3 to 1.2 mol %) in terms of Mn2O3, a copper oxide in an amount of 2.0 to 8.0 mol % (particularly preferably 3.0 to 7.0 mol %) in terms of CuO, zinc oxide in an amount of 30.1 to 33.0 mol % (particularly preferably 30.1 to 32.0 mol %) in terms of ZnO and a nickel oxide in mol % in terms of NiO as the balance.
Further, the ferrite material of the present invention also contains a bismuth oxide in an amount of 0.5 to 6.0 wt % (particularly preferably 0.5 to 5.0 wt %) in terms of Bi2O3, a silicon oxide in an amount of 0.1 to 2.0 wt % (particularly preferably 0.15 to 1.5 wt %) in terms of SiO2 and a magnesium oxide in an amount of 0.05 to 1.0 wt % (particularly preferably 0.05 to 0.8 wt %) in terms of MgO, in addition to the above main components.
Talc contains Si and Mg in predetermined proportions as sintering components. Therefore, talc can be added in place of the above SiO2 and MgO. In that case, to satisfy the above amounts of SiO2 and MgO, talc is added in an amount of 0.15 to 3.2 wt %.
In the above composition, when the content of Fe2O3 is lower than 47 mol %, the inconvenience that initial permeability lowers occurs, while when the content of Fe2O3 is higher than 50.0 mol %, the inconvenience that a quality coefficient Q becomes smaller occurs. When the content of Mn2O3 is lower than 0.3 mol %, the inconvenience that the initial permeability lowers occurs, while when the content of Mn2O3 is higher than 1.5 mol %, the inconvenience that the quality coefficient Q becomes smaller occurs. When the content of CuO is lower than 2.0 mol %, the inconvenience that the initial permeability lowers occurs, while when the content of CuO is higher than 8.0 mol %, the inconvenience that the quality coefficient Q becomes smaller occurs.
When the content of ZnO is lower than 30.1 mol %, the inconvenience that the initial permeability lowers occurs, while when the content of ZnO is higher than 33.0 mol %, the inconvenience that a Curie point becomes lower is liable to occur.
When the content of Bi2O3 is lower than 0.5 wt %, a sintered density becomes lower, so that the inconvenience that the strength of a sintered body lowers occurs. On the other hand, when the content of Bi2O3 is higher than 6.0 wt %, the inconvenience that the quality coefficient Q becomes smaller is liable to occur.
When the content of SiO2 is lower than 0.1 wt %, the quality coefficient Q is liable to become smaller, while when the content of SiO2 is higher than 2.0 wt %, the initial permeability is liable to lower.
When the content of MgO is lower than 0.05 wt %, the quality coefficient Q is liable to become smaller, while when the content of MgO is higher than 2.0 wt %, the initial permeability is liable to lower.
As for the case where the above SiO2 and MgO are substituted by talc, when the content of talc is lower than 0.15 wt %, the quality coefficient Q is liable to become smaller, while when the content of talc is higher than 3.2 wt %, the initial permeability is liable to lower.
In the present invention, to the above main components, CoO may also be added in an amount of 0.02 to 0.6 wt %, particularly preferably 0.05 to 0.5 wt %, as an additional component. Although CoO is added primarily for increasing the quality coefficient Q, the initial permeability lowers when the amount of CoO becomes too large and exceeds 0.6 wt %.
The NiCuZn-based ferrite material of the present invention relates to a ferrite material having an initial permeability xcexci of not lower than 200. Primarily, it is suitably used in such an application as a tuning coil which requires a high Q value in a band ranging from 0.1 to 2.0 MHz.
The ferrite material of the present invention, for example, is molded into a core material having a predetermined shape, wrapped around by necessary windings and then resin-molded (resin-coated) to be used as a fixed inductor, a chip inductor or the like. These are used, for example, as a variety of electronic equipment in mobile communication devices such as a television, a video recorder, a portable telephone and an automobile telephone. The shape of the core is not particularly limited. An example of the core is a drum-type core having an external diameter of not larger than 2 mm and a length of not larger than 2 mm.
A resin used as a molding material (coating material) may be a thermoplastic or thermosetting resin, for example. Specific examples of the resin include a polyolefin, a polyester, a polyamide, a polycarbonate, a polyurethane, a phenol resin, an urea resin and an epoxy resin. Illustrative examples of means for molding the molding material include dipping, coating, spraying, injection molding and cast molding.
An example of the constitution of a chip inductor using the ferrite material of the present invention will be presented below. For example, the chip inductor comprises a cylindrical core molded from the ferrite material of the present invention and having a large-diameter rig on both sides, a winding wound around the barrel of the core, electrode terminals disposed on both sides of the core for connecting the edges of the wiring to an external electric circuit and fixing the core in a resin, and a resin molded to cover these components.
Next, a description will be given to an example of a method for producing a ferrite by using the ferrite material of the present invention.
Firstly, a mixture is prepared by mixing predetermined amounts of raw materials as the main components with predetermined amounts of raw materials as the additional components such that the proportions of these components in the mixture fall within the ranges specified by the present invention.
Then, the mixture is calcined. The calcination is carried out in an oxidizing atmosphere, for example, in the air. The calcination temperature is preferably 800 to 1,000xc2x0 C., and the calcination time is preferably 1 to 3 hours. Then, the resulting calcined mixture is milled by a ball mill or the like to predetermined sizes. When the mixture is milled, raw materials as the additional components may be added to and mixed into the mixture. Further, the raw materials as the additional components may be added such that some of the raw materials are added before the calcination and the rest of them are added after the calcination.
After the calcined mixture is milled, an appropriate amount of binder such as a polyvinyl alcohol is added and the resulting product is molded into a desired shape.
Then, the molded compact is sintered. The sintering is carried out in an oxidizing atmosphere, generally in the air. The sintering temperature is about 950 to 1,100xc2x0 C., and the sintering time is about 2 to 5 hours.
The present invention will be described in more detail with reference to specific examples.